Sputtering Power on the Microstructure and Properties of MgF2 Thin Films Prepared with Magnetron Sputtering

Abstract

To reduce the F deficiency defect in MgF2 thin films deposited with magnetron sputtering, SF6 was added to the working gas Ar2 as the reactive gas, and MgF2 thin films were prepared on quartz glass substrates with radio frequency (RF) magnetron sputtering. The effects of sputtering power on the chemical compositions, microstructure and optical properties of MgF2 thin film were investigated. The results show that with sputtering power increase from 115 to 220 W, the atomic ratio of F to Mg increased continuously, and reached 2.02 at 185 W, close to ideal stoichiometric ratio of 2 : 1. The crystallinity of MgF2 film improved first, then decreased, and finally changed into amorphous state. Profile of particles composing MgF2 film became clearer at first, and finally became blurred. Refractive index of MgF2 film decreased firstly and then increased, and got the lowest value at 185 W, 1.384 at 550 nm wavelength which is very close to that of MgF2 bulk crystal. The integral transmittance of the coated glass within 300-1100 nm (hereinafter referred to as the transmittance of the thin film) increased first and then decreased, and reached 94.99% at 185 W, higher than that of the bare glass substrate by 1.79%.